This invention relates to a sensor and system that is used to monitor and analyse electrocardiogram signals remotely from patients located in non-hospital sites.
As used herein, the term "electro-cardiogram" (ECG) refers to an electrical signal from the heart which may be measured from two or more sensors placed on the patients skin, either on a limb or about the patient's thorax.
The term "complex" refers to a period of ECG signal which, when voltage amplitude is plotted against time, exhibits a shape which may be repeated in other epochs. Typically, a complex will include a particular amplitude maxima or minima which is termed the detect point. The rate at which detect points occur in a particular ECG signal is the same as the heart rate. The term `normal complex` refers to a complex in an ECG signal that is regularly repeated and is measured at electrodes placed on a person whose heart is beating in Normal Sinus Rhythm (NSR). The shape of a normal complex may vary from patient to patient and between ECG signals recorded from different sites on the same patient.
The terms P, Q, R, S and T when used herein in relation to ECG complexes refer to portions of a normal complex that relate to particular electro-physiological events in the cardiac cycle.
The term "normal rate" for a particular patient refers to a range of heart rates that is typical for a healthy individual of similar age to the patient when at rest.
The term "arrhythmia" relates to an abnormal rhythm of the heart that persists for multiple complexes which may or may not revert to normal sinus rhythm spontaneously. An arrhythmia may be made up of normal complexes at a rate that is abnormally high for the patient or abnormally low or, alternatively, an arrhythmia may consist of abnormal complexes at a high, low or normal rate.
In known systems, the patient is provided with sensors attached to the patient's body and which are coupled by electrical leads to an event recorder. The event recorder then sends the ECG signals to the monitoring system via a telecommunications line, e.g. a telephone line.
A major disadvantage of these known systems is that continuous monitoring of a patient has been met with a distinct lack of enthusiasm by the patient due to the need for a lead to connect the sensors to the event recorder. This causes discomfort and difficulties in dressing and washing, and also some embarassment as it is difficult to hide from view.